Project Summary: SUMO is a ubiquitin-like protein that is reversibly conjugated to a wide variety of target proteins, thereby serving as a flexible switch to control protein subcellular localization and biochemical activity. SUMO conjugation ("sumoylation") plays central roles in many crucial biological processes including epigenetic inheritance and pattern formation. The long-term goal of this research is to illuminate the connections between sumoylation and these biological phenomena using the easily manipulated model organism Drosophila melanogaster. The specific aims are: 1. To determine the role of SUMO in Polycomb Group (PcG) function. PcG factors play essential roles in maintaining the silent epigenetic state of genes that regulate development. Two PcG factors, Ph and Scm, appear to be regulatory targets of sumoylation. Genetic, cell biological, and biochemical approaches will be employed to make mechanistic connections between the sumoylation of these proteins and transcriptional silencing. 2. To carry out a system wide analysis of the effects of genotype and developmental stage on the spectrum of SUMO-conjugated proteins. The pleiotropic roles of SUMO suggest the existence of many unidentified SUMO conjugation targets. Proteomic techniques will be used to characterize the spectrum of SUMO conjugated proteins in the intact organism as a function of genotype and developmental stage. The creation of a multi-dimensional database of SUMO-conjugated proteins will allow us to test hypotheses about how SUMO conjugating and deconjugating enzymes determine the specificity of conjugation, and about the role of SUMO in such processes as protein biogenesis, epigenetic transcriptional control, and embryogenesis. Relevance: The sumoylation pathway has been implicated in both neurodegenerative disorders and cancer. For example, sumoylation of Huntingtin, the pathogenic protein in Huntington's disease, exacerbates neurodegeneration in a Drosophila model of this disease. Furthermore, the sumoylation of numerous oncoproteins (c-jun, elk-1, and TEL) and tumor suppressor proteins (p53, RB, and PML) modulates their function. Consequently, the research proposed here will advance our understanding of human disease.